He should have run a vent pipe from the lower system up to the piping on the upper floor. The way it was done should work in your case, but in a different situation, flushing an upper toilet could cause the water in the lower toilet to either blow out of the bowl, or be sucked down the drain. Neither situation not being particularly desirable.

: hi terry,

: i am remodeling my basement - and putting in a bathroom (toilet, corner: shower and sink). The plumber has hooked up my toilet: to the main vent/stack from my bath upstairs. While: I have asked a couple of times about this - I still "don't: get it". Could you explain this wet vent thing to me and : ensure me that it is ok.